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Whittaker's last year signed Lawson to promote its new 5 Roll refined chocolate in a TV ad campaign. The company, which prides itself on its family-friendly and trustworthy image, said Lawson's contract with it had ended in October.

Marketing manager Holly Whittaker said no decision had been made about continuing use of the star, but the company had no plans to run the commercial again.

"We chose Nigella because she is widely liked for her warm and refined manner," Whittaker told the Herald on Sunday. "What happened is disappointing, but we are remaining neutral at this stage. What happens in Nigella's personal life is out of our control, but that is the risk you take when engaging with celebrities."

Whittaker said the drug-taking allegations had been discussed "briefly" at a senior level, but the company had received no complaints from customers.

Canterbury University associate marketing professor Ekant Veer said companies seeking celebrity endorsement looked for people who were a good match with the brand.

"In this case - Whittaker's, Nigella Lawson, decadent, sexy, cool, sweet - it all makes sense. Throw cocaine in there, and suddenly it doesn't seem to make so much sense."